def foo : A → B → B :=
fun a b => { x := a.x, y := b.y }
def boo : A → B → B :=
fun a b => { x := b.x, y := b.y }
def baz : A → B → C :=
fun a b => { toB := { x := a.x, y := b.y } }
def biz : A → B → C :=
fun a b => { toB := b }
def faz : A → C → C :=
fun a c => { toB := { x := a.x, y := c.y } }
def fiz : A → C → C :=
fun a c => { toB := c.toB }